The present invention relates to a new and improved control apparatus for an electromagnetic brake of a weaving machine.
Generally speaking, the control apparatus of the present development is of the type comprising at least one switching stage for generating a continuous signal which indicates a braking function and at least one switching stage for generating a pulse signal which is released at a given crank angular position of the machine, wherein the switching stage for the continuous signal and the switching stage for the pulse signal are conjointly connected to an AND-gate or circuit supplying or triggering a stop pulse for the brake device or unit which is arranged thereafter.
In order to achieve the shortest possible braking angles, the electromagnetically actuatable band or jaw brakes used with textile machines as well as the electromagnetic single disk brakes can be over energized or quickly energized by various types of switch means. In the context of this disclosure the term "braking angle" refers to the angle of rotation of the machine crankshaft or crank from the moment the electrical stop signal is generated until the complete standstill of the machine.
Especially with weaving machines or looms it becomes necessary that the loom after the braking of the crankshaft or crank comes to standstill in a clearly defined position, i.e. the so-called angular position of the crank or crankshaft, so that subsequent working cycles can be started or carried out effortlessly. For instance, after a stop following a weft thread rupture the weaving machine should stand still with the shed open, so that the weft thread rupture can be quickly repaired. On the other hand, after a stop of the loom following a warp thread rupture, the machine has to come to a stop with the shed closed. Furthermore, other angular positions of the crankshaft are conveivable at the machine, depending upon the given machine function.
In order to attain such given angular positions of the crankshaft at a weaving machine as a function of the specific branking function, such as normal loom shutdown or stop, warp thread rupture, weft thread rupture or the like, there are used control apparatuses of the initially mentioned type, wherein the braking process invariably starts from the same preadjusted angular position of the crankshaft and also ends there, provided that the braking angle at the machine shaft remains the same. The brake pulse transmitters which are used either comprise cams which are adjustable in peripheral direction at the main shaft of the machine according to each braking function. These cams cooperate with stationary switches or switches which are adjustably arranged at the main shaft of the machine and cooperate with stationary cams.
However, such multiple switch arrangements are not only expensive, but as a result of the common and frequent changes of the operating conditions at such machines also require a considerable adjustment or setting expenditure, expecially since the switches are, as a rule, arranged under covereings of the machine and at locations where access is difficult. In addition, a readjustment or fine adjustment at the switches for achieving a most precise adjustment or readjustment of the angular position of the crankshaft according to each braking function is almost impossible.
In German Pat. no. 2,825,969 published Dec. 20, 1979, proposals have been made to generate the stop pulses by digital preselection circuits at incremental or coded transmitters for the angle of the crank or crankshaft. However, this solution requires great and very expensive circuit expenditure.